Fastener driving tool

ABSTRACT

A pneumatic piston-driver blade return system for a pneumatic fastener driving tool includes an air return space continuously communicating with the lower end of a cylinder immediately adjacent a bumper. When a top valve for the cylinder is opened, compressed air drives the piston downwardly against the bumper, and a part of this air is passed through the piston into the air return space by means of an O-ring valved passage through the piston. When the cylinder top valve is closed and the top of the cylinder is vented to the atmosphere, the air in the return space enters the cylinder and acts on the lower surface of the piston to return the piston-driver blade to a normal position in which it is held by frictional engagement of another piston O-ring with the cylinder wall. Air below the piston leaks out to the atmosphere through a driver blade clearance at the lower end of the cylinder.

United States atent [151 3,673,922 Doyle 1 1 July 4, 1972 [54] FASTENERDRIVING TOOL Primary Examiner-Carroll B. Dority, Jr. [72] Inventor.Richard H. Doyle, Mount Prospect, 11]. Atmmey Mason Kolehmainen' Rathbum& y [73] Assignee: Fastener Corporation, Franklin Park, Ill. 22 Filed:Dec. 19,1966 [57] ABSTRACT [21] APPLNOJ 602 728 A pneumaticpiston-driver blade return system for a pneumatic fastener driving toolincludes an air return space continuously communicating with the lowerend of a cylinder im- [52] U.S. Cl ..9l/422, 91/461, 92/183, mediatelyadjacent a bumper. When a top valve for the 227/130 cylinder is opened,compressed air drives the piston [5 downwardly against the bumper and apan of this air is passed Fle'd of Search 9 1 5, through the i ton intothe air return space means of an 0- 91/422, 426, 461; 92/30, 16 171, 183ring valved passage through the piston. When the cylinder top valve isclosed and the top of the cylinder is vented to the at- [56] Referencescued mosphere, the air in the return space enters the cylinder andUNITED STATES PATENTS acts on the lower surface of the piston to returnthe pistondriver blade to a normal position in WhlCh it 15 held by fric-1,771,219 7/1930 l-lem ..92/3O X tional engagement of another pistonO-ring with the cylinder 3,106,136 10/1963 Langas "mm/417 wall. Airbelow the piston leaks out to the atmosphere through i g f a driverblade clearance at the lower end of the cylinder. ugm 3,363,517 1/1968Powers ..9l/422 X 15 Claims, 4 Drawing Figures 8 41K" M? 20 ifi/ 4 /0Z12 7 a2 66 a 31.1 a 15.1: $1 1 :gs \\\\\S i!| 9a s M FAS'IENER DRIVINGTOOL This invention relates to a fastener driving tool and, moreparticularly, to a'fastener driving tool including new and improvedpiston return means for returning the piston after the completion of apower or driving stroke.

Commercial pneumatic fastener driving tools on the market today arecommonly of the type including pneumatic means for returning the pistonafter the completion of a fastener driving stroke. Such tools arefrequently operated by a trigger actuated pilot valve that functionswhen the trigger is depressed to move the drive piston and connectedfastener driving blade through a power or drive stroke of a fastenerdriving operation by the admission of pressurized fluid into thecylinder of the tool. The drive piston will generally remain at the endof its power stroke until the fluid pressure in the cylinder isreleased, as by exhausting the cylinder to atmosphere, at which time thepiston return means is efiective to return the piston to its normal orstatic position. Commercially available fastener driving tools mayeither return upon release of the trigger actuated pilot valve, or thedrive piston and driving blade of such tools may move both down and upautomatically upon a single depression of the trigger, before thetrigger is released. In both types of control means are provided forsupplying pneumatic fluid below the piston for returning the piston toits normal or static position after the air above the piston has beenexhausted. The. piston must remain in its normall or static positionuntil it is again driven through a fastener driving stroke.

One object of the present invention is to provide a new and improvedpneumatic return means for a fastener driving apparatus.

Another object of the present invention is to provide a fastener drivingapparatus including new and improved pneumatic return means forreturning the drive piston and associated driver blade to the nonnal orstatic position upon exhaustion of the fluid from above the piston.

Yet another object of the present invention is to provide an improvedmeans for holding the piston of a fastener driving too] in its normal orstatic position during its rest between fastener driving operation.

Yet another object of the present invention is to provide a new andimproved pneumatically actuated fastener driving tool.

In accordance with these and many other objects, there is provided apneumatically operated fastener driving too] of the type including ahousing having a cavity defining a fluid reservoir, and a cylinder inthe housing. A drive piston is slidably mounted in the cylinder. Asuitable cylinder valve may be provided for controlling the admission offluid and for the exhaustion of fluid from the end of the cylinder abovethe piston. The cylinder valve may operate under the control of a pilotvalve, or the fastener tool may be of the snap action or automaticsignal stroke type. In accordance with the present invention, a pistonreturn reservoir is provided in the housing and air passage meansinterconnect the piston return reservoir and the cylinder adjacent thelower or other end of the cylinder. The piston is provided with a pairof spaced peripheral grooves in its outer wall and a sealing member iscarried in one of the grooves toward the open or control end of thecylinder effecting a pneumatic seal between the piston and the cylinder.A resilient ring sealing member, which may be of the O-ring type, iscarried in the other of the grooves. Air passage means in the pistonextend from the bottom of this groove to above the piston to provide abypass around the upper one of the peripheral grooves. The sealingmember functions as a check or one way valve so that upon a selectedpressure differential between the upper and lower ends of the cylinder,the resilient ring sealing member will be effective to unseat from theair passage openings to provide for fluid bypass around the firstsealing member.

It will be understood that during the driving stroke of the piston, thepressure above the piston does not build up sufficiently to unseat thelower O-ring of the piston and permit bypass of the pressurized fluidaround the piston. However,

once the piston has reached the end of its power stroke and the pressureabove the piston continues to build up, the pressure will unseat thelower O-ring to flow into the piston return reservoir. The lower O-ringwill then reseat itself to close the bypass around the piston andprovide the pneumatic fluid for the return stroke of the piston.

In accordance with another feature of this invention the open end of thecylinder above the piston has an enlarged diameter to define a shoulderwith the remainder of the cylinder, and the upper sealing member, whichmay also be an O-ring, will expand above the shoulder to retain thepiston in its normal or static position during its rest between fastenerdriving strokes.

Many other objects and advantages of the present invention will becomeapparent from the following detailed description, when given inconnection with the accompanying drawings in which:

FIG. 1 is a fragmentary cross-sectional view of a fastener driving toolincorporating the improved pneumatic return mechanism according to thepresent invention and illustrated with the drive piston and driver bladein its static or at rest position;

FIG. 2 is a fragmentary cross-sectional view of the fastener drivingtool of FIG. 1, illustrated with the drive piston and driver blade atthe end of the drive stroke;

FIG. 3 is a fragmentary cross-sectional view of the piston in thecylinder illustrating the groove and O-ring forming the valve member andtaken along line 3-3 of FIG. I; and

FIG. 4 is an isometric fragmentary cross-sectional view of the grooveand O-ring forming the valve member in the lower one of the grooves onthe piston and taken along line 4-4 of FIG. 3.

Referring now to the drawings, there is fragmentarily illustrated afastener driving tool, generally illustrated as 10, which embodies thepresent invention. The tool 10, as illustrated, comprises a housing 12including a generally vertically extending head or forward portion 12aand a rearwardly extending handle portion 12b defining a fluid reservoir16. Pressurized fluid, such as compressed air, is supplied to the fluidreservoir of the tool by suitable means, not illustrated. The drivesystem for the tool 10 includes a main cylinder 18 slidably mountedwithin a cavity 12c in the head portion and having an open upper end 18athat is adapted to be selectively connected to the reservoir 16 and tothe atmosphere. The open upper end of the cylinder 18 is normally inengagement with a diaphragm type main or cylinder valve assembly 20under the control of a trigger pilot valve assembly 24. Slidably mountedwithin the cylinder 18 is a power or drive piston 26 having connectedthereto a depending driver blade member 28. An exhaust valve assemblyindicated generally as 32 is provided for controlling the selectiveconnection of the upper end of the cylinder 18 to the atmosphere.

When the tool 10 is to be operated, the trigger pilot valve assembly 24is actuated so that the compressed fluid from the reservoir 16 entersthe upper end of the cylinder 18 and drives the fastener drive piston 26downwardly to engage a fastener or nail supplied to a drive track in anosepiece or nosepiece structure 36. The flow of compressed fluid intothe upper end of the cylinder 18 is controlled by the cylinder valveassembly 20, which includes a diaphragm 40, the periphery of which isclamped between a cap 42 and the head portion 12a of the housing 12 andwhich seats against the upper edge 18a of the cylinder 18. The diaphragm40 is resiliently biased against the upper edge surface 18a by a spring44 located between the cap 42 and the diaphragm 40. The cylinder side ofthe diaphragm 40 is continuously in connection with the fluid reservoir16 through a suitable passageway 46 and annular chamber 47 so that thepressurized fluid continuously acts against the cylinder side of thediaphragm 40 tending to displace the diaphragm 40 from the edge 18a ofthe cylinder 18. However, pressurized fluid is also introduced to theopposite side of the diaphragm 40 through a passageway 48 when thefastener driving tool 10 is in a static or at rest position. Thedifferential pressure acting upon the diaphragm 40 is efi'ective tomaintain the diaphragm 40 in a closed position, as illustrated inFIG. 1. However, as the pressurized fluid above the diaphragm 40 isdischarged, the pressurized fluid acting through passageway 46 iseffective to unseat the diaphragm 40 from the edge 18a of the cylinder18 to direct pressurized fluid into the top of the cylinder 18 and todrive the drive piston 26 through a drive stroke.

When the fastener driving tool is at rest, or during the return strokeof the drive piston, the upper open end of the cylinder 18 is exhaustedto the atmosphere through the exhaust valve assembly 32. In theillustrated embodiment the exhaust valve assembly comprises a hollowvalve stem 50 secured to the diaphragm and connecting the upper end ofthe cylinder 18 to the atmosphere through a suitable exhaust passageway52. However, when the drive piston is operated through a fired or drivestroke, it is necessary for the upper end of the cylinder 18 to beclosed 011 from the atmosphere, and to this end there is provided avalve seat 54 on the cap 42 disposed adjacent the end of the valve stem50 remote from the cylinder 18 and adapted to be engaged by the valvestem 50 when the diaphragm 40 is raised at the initiation of a drivestroke, thereby closing off the upper end of the cylinder 18 to theatmosphere. Since a substantial impact load is transmitted to the valveseat 54, the cap 42 is preferably of hardened steel. Advantageously ahardened steel cap 42 will prevent damage occurring to the tool if theoperator thereof taps with the cap 42.

The trigger pilot valve assembly 24 is provided for initiating thefiring of the tool 10, and may be of known design. in the illustratedembodiment the valve assembly 24 includes a valve chamber 58 havingopposed valve ports 60 and 62 defining valve seats alternatelyengageable by a valve element 63 here shown as comprising a valve ball64 and a downwardly extending rod actuator 66. The valve port 60communicates with the reservoir 16, while the valve port 62 exhausts thevalve chamber 58 to the atmosphere when the valve ball 64 is unseatedtherefrom. The rod actuator 66 is operated by a suitable trigger 68 sothat when the fastener driving tool 10 is at rest the valve ball 64 isseated against the valve port 62, and when the trigger 68 is depressed,the valve ball 64 closes the valve port 60. Additionally, the pilotvalve chamber 58 is provided with a control port 70 connected to theupper end of the cylinder valve assembly 20 through the passageway 48.It will be understood that in the operation of the trigger pilot valve,when the trigger 68 is released, the control port 70 is in communicationwith the reservoir 16 through the valve port 60; but when the trigger 68is depressed unseating the valve ball 64 from the valve port 62 andclosing the valve port 60, the control port 70 is exhausted to theatmosphere.

To provide for the return drive of the drive piston 26, there isprovided an air return chamber 76 communicating with the lower end ofthe cylinder 18 through a plurality of air passage openings 78 includingports 78a opening in the cylinder 18. The piston 26 is of generallycup-shape with a central cavity 26a opening toward the upper end of thecylinder 18. The outer surface of the piston 26 is provided with spacedperipheral grooves 82 and 84, the upper one 82 of which serves as asealing groove while the lower one 84 functions as a one way valve meansto provide for the passage of pressurized fluid to the air returnchamber 76. An O-ring 86 provided in the upper one of the grooves 82functions as a sealing member effecting a pneumatic seal between thepiston 26 and the inner wall of the cylinder 18. To bypass around thegroove 82 and O-ring 86, there is provided a plurality of airpassageways 90 extending from the lower one of the grooves 84 andcommunicating with the central cavity 26a. An O-ring 92 defining a valveelement is positioned within the lower one of the grooves 84. The O-ring92 is of resilient construction and is normally seated against the portsdefined by the air passages 90. To this end, the O-ring 92 in itsunstressed state has an inner diameter d, shown in phantom in FIG. 3,smaller than the inner diameter D of the groove 84 and has a diametricthickness t, FIG. 4, less than the width T of the groove 84. The Q-ring92 is expandable upon a selected pressure differential between the upperand lower ends of the cylinder through the piston 26 so as to unseatfrom the ports a of the air passages 90 to provide for fluid to bypassthrough the piston 26 around the O'ring 92 and to supply air to the airreturn chamber 76.

It is of course necessary to seal the driver blade 28 suffrciently totrap the air for the return stroke and to this end there is provided asealing washer 77 at the lower end of the head 12a and having an opening77a closely receiving the blade 28. It is necessary to providesufficient air to return the piston 26, but the volume of return airshould not be so great as to require an excessive air supply or toprevent rapid discharge of the return air by leakage through the opening77a after return of the piston 26. It has been found that a ratio ofreturn air to piston displacement of two-thirds is satisfactory.

To cushion the drive stroke of the piston 26 and to provide a furtherpneumatic seal around the driver blade when the drive piston 26 is inits lowermost position, there is provided a resilient annular bumper 96at the lower end of the cylinder 18 which is engageable by the piston26, as illustrated in FIG. 2, when the piston 26 is in its lowermostposition.

Advantageously the cylinder 18 is held in position in the cavity only bythe fluid pressure acting upon it, thus facilitating rapid disassemblyfor repair or replacement. More specifically, the cylinder 18 includesan outwardly extending flanged portion 18b adjacent an inwardlyextending ring portion 12d formed in the wall of the cavity 120. Theinterface between the flanged portion 18b and the portion 12d is sealedby a resilient O-ring 98 so that the O-ring 98 divides the space betweenthe wall of the head portion 120 and the cylinder 18 into the chambers47 and 76. The lower end of the cylinder 18 is provided with anoutwardly extending flange 18c engageable against the inner surface ofthe cavity 120 to position the lower end of the cylinder 18. The fluidpressure in the chamber 47 acts on the outwardly extending flangedportion 18b to hold the cylinder 18 in place. The spaced positioning ofthe work cylinder 18 from the wall of the head portion 120 furtherserves to protect the cylinder 18 against damage by impact or otherforces on the head 12a of the tool 10.

To hold the piston 26 of the fastener driving tool 10 in its static ornormal position during the rest period between fastener drivingoperations, the upper O-ring 86 locks against a shoulder 18d formed atthe lower end of an enlarged diameter portion 18c in the cylinder 18.Preferably the shoulder 18d is chamfered to provide an incline for theO-ring 86.

From the above-detailed description, the operation of the improvedpneumatic return system is believed clear. However, briefly, it will beunderstood that in the operation of the basic tool, the piston 26 andassociated driver blade member 28 is driven downwardly through a drivestroke by the connection of the open upper end of the cylinder 18 withthe reservoir 16. Since there is not significant restraint to the piston26 during its downward movement, the pressure above the piston 26 willnot build up sufliciently to unseat the O-ring 92 until the piston 26reaches the bottom of its drive stroke as illustrated in FIG. 2. At thispoint the pressure above the piston 26 will continue to build up untilit approaches the pressure in the reservoir 16 and the O-ring 92,functioning as a valve element, will be unseated from the ports of theair passages 90 thereby providing a source of pressurized fluid to theair return chamber 76 through the air passage opening 78. There will beno significant loss of air below the piston 26 during the short timeinterval required for the drive and return strokes of the piston. Uponrelease of the trigger 68 the cylinder valve assembly 20 will closeagainst the open upper end 18a of the cylinder 18 and the upper end ofthe cylinder 18 will be exhausted to the atmosphere through the exhaustvalve assembly 32. At this time the pressurized fluid in the air returnchamber 76 will return through the openings 78 below the piston 26 andwill return the piston 26 and associated driver blade member 28 to itsstatic or at rest position. The return air will then exhaust around thedriver blade 28 through the opening 77a to prepare the tool for asubsequent driving stroke.

Although the present invention has been described by reference to asingle embodiment thereof, it will be apparent that numerous othermodifications and embodiments may be devised by those skilled in the artand it is intended by the appended claims to cover all modifications andembodiments which will fall within the true spirit and scope of thepresent invention.

What is claimed as new and desired to be Patent of the United States is:

l. A pneumatically operated fastener driving too] comprising a housinghaving a cavity defining a fluid reservoir, a cylinder in said housing,a piston slidably mounted in said cylinder, a cylinder valve means forcontrolling the admission of fluid and for the exhaustion of fluid fromone end of said cylinder, a piston return reservoir in said housing, airpassage means connecting said piston return reservoir and said cylinderand including port means opening in said cylinder adjacent the other endthereof, said piston including a pair of spaced peripheral grooves inits outer wall, a ring sealing member in the one of said grooves towardsaid one end of said cylinder efiecting a pneumatic seal between saidpiston and said cylinder, air passage means in said piston extendingfrom the other of said grooves around said one of said grooves andincluding means defining ports in said other of said grooves, aresilient ring sealing member in said other of said grooves normallyseated against said ports and expandable upon a selected pressuredifferential between said one end of said cylinder and said other endthereof to unseat from said ports to provide for fluid to bypass aroundthe first sealing member from said one end of said cylinder to saidother end thereof providing for passage of air into said piston returnreservoir.

2. A fastener driving tool as set forth in claim 1 wherein said lastmentioned sealing member is an O-ring.

3. A fastener driving tool as set forth in claim 2 wherein the insidediameter of said O-ring in its unstressed state is less than the minimumdiameter of said other of said grooves, and the diametrical thickness ofsaid O-ring is less than the width of said other of said grooves.

4. A fastener driving tool as set forth in claim 1 wherein said pistonis generally cup-shaped with a central cavity opening toward said oneend of said cylinder and said air passage means comprises a plurality ofpassageways communicating between the inner surface of said other ofsaid grooves and said cavity.

5. A fastener driving too] as set forth in claim 1 and including aresilient annular bumper adjacent said other end of said cylinderengageable by said piston and defining a pneumatic seal when said pistonis at said other end of said cylinder.

6. A fastener driving tool as set forth in claim 1 wherein said cylinderis provided with an enlarged diameter portion at its upper end defininga shoulder, and wherein said ring sealing member sets above saidshoulder when said piston is in its normal position to retain the pistonin said normal position.

7. A pneumatically operated fastener driving tool comprising a housinghaving a cavity defining a fluid reservoir, a cylinder in said housinghaving an open upper end and an enlarged diameter portion forming ashoulder with the remainder of said cylinder and extending from saidshoulder to the open upper end of the cylinder, a piston slidablymounted in said cylinder and provided with at least one peripheralgroove in its outer wall, a ring sealing member in said groove effectinga pneumatic seal between said piston and said cylinder and setting abovesaid shoulder when said piston is in its normal position thereby holdingsaid piston in said normal position, a cylinder valve means forcontrolling the admission of fluid and the exhaustion of fluid from theopen upper end of said cylinder, said cylinder valve means includingstructure engaging the piston to stop the piston in said normalposition, the shoulder in the cylinder being spaced downwardly from theopen upper end thereof a distance such that the ring sealing memberrests on the shoulder when the piston engages secured by Letters thestructure on the cylinder valve means, and means controlling operationof said cylinder valve.

8. In combination:

a. a single stroke fluid pressure operated motor having a cylinder witha piston operable therein between a retracted position at one end of thecylinder and an actuated position at the other and closed end of thecylinder, and with a driver extended from the piston and through a closefitting limited leakage guideway at the said other closed end of thecylinder;

. means operable to charge and to exhaust the cylinder at said one endthereof;

c. restraining means normally holding the piston at rest at saidretracted position;

. a closed fluid reservoir in open and continuous communication with thecylinder below the piston throughout its travel between said retractedand actuated positions;

e. and air return means for movement of the piston from said actuatedposition to said retracted position when the first mentioned means isoperated to exhaust the cylinder and comprising, a fluid restrictingport through the piston and communicating with the fluid under pressureadvancing the piston and open into said reservoir below the piston whenthe first mentioned means is operated to charge the cylinder;

f. whereby there is a build-up of fluid pressure in the reservoir as thepiston reaches the said actuated position, and

whereby the built-up fluid pressure is applied to the piston and returnsthe same to the retracted position when the first mentioned means isoperated to exhaust the cylinder followed by exhaust of said built-uppressure through said limited leakage guideway.

9. In combination:

a. a single stroke fluid pressure operated motor having a cylinder witha piston operable therein between a retracted position at one end of thecylinder and an actuated position at the other and closed end of thecylinder, and with a driver extended from the piston and through a closefitting limited leakage guideway at the said other closed end of thecylinder;

b. means operable to charge and to exhaust the cylinder at said one endthereof;

c. restraining means normally holding the piston at rest at saidretracted position;

. a closed fluid reservoir in open and continuous communication with thecylinder below the piston throughout its travel between said retractedand actuated positions;

e. and air return means for movement of the piston from said actuatedposition to said retracted position when the first mentioned means isoperated to exhaust the cylinder and comprising, a fluid restrictingcheck valve means through the piston and communicating with the fluidunder pressure advancing the piston and open into said reservoir belowthe piston when the first mentioned means is operated to charge thecylinder; whereby there is a build-up of fluid pressure in the reservoiras the piston reaches the said actuated position, and whereby thebuilt-up fluid pressure is applied to the piston and returns the same tothe retracted position when the first mentioned means is operated toexhaust the cylinder followed by exhaust of said built-up pressurethrough said limited leakage guideway.

10. In combination:

a. a single stroke fluid pressure operated motor having a cylinder witha piston operable therein between a retracted position at one end of thecylinder and an actuated position at the other and closed end of thecylinder, and with a driver extended from the piston and through a closefitting limited leakage guideway at the said other closed end of thecylinder;

b. means operable to charge and to exhaust the cylinder at said one endthereof;

c. restraining means normally holding the piston at rest at saidretracted position;

d. a closed fluid reservoir in open and continuous conununication withthe cylinder below the piston throughout its travel between saidretracted and actuated positions;

e. and air return means for movement of the piston from said actuatedposition to said retracted position when the first mentioned means isoperated to exhaust the cylinder and comprising, a port through thepiston and communicating with the fluid under pressure advancing thepiston, a valve seat surrounding the piston and carrying a constrictedcheck valve element to yieldingly open the port into the cylinder belowthe piston and into said reservoir when the first mentioned means isoperated to charge the cylinder;

f. whereby there is a build-up of fluid pressure in the reservoir as thepiston reaches the said actuated position, and whereby the built-upfluid pressure is applied to the piston and returns the same to theretracted position when the first mentioned means is operated to exhaustthe cylinder followed by exhaust of said built-up pressure through saidlimited leakage guideway.

l 1. In combination:

a a single stroke fluid pressure operated motor having a cylinder with apiston operable therein between a retracted position at one end of thecylinder and an actuated position at the other and closed end of thecylinder, and with a driver extended from the piston and through asubstantially close fitting limited leakage guideway at the said otherclosed end of the cylinder;

b. means operable to charge and to exhaust the cylinder at said one endthereof;

c. restraining means normally holding the piston at rest at saidretracted position;

d. a snubber means comprising a body of resilient material surroundingthe driver and with a seat having sealed engagement with the bottom ofthe piston upon arrestment of the piston at said actuated position;

e. a closed fluid reservoir in open and continuous communication withthe cylinder above said snubber seat and below the piston throughout itstravel between said retracted and actuated positions;

f. and air return means for movement of the piston from said actuatedposition to said retracted position when the first mentioned means isoperated to exhaust the cylinder and comprising, a fluid restrictingport through and opening above the bottom of the piston andcommunicating with the fluid under pressure advancing the piston andopen into said reservoir when the first mentioned means is operated tocharge the cylinder;

g. whereby there is a build-up of fluid pressure in the reservoir as thepiston reaches the said actuated position, and whereby the built-upfluid pressure is applied to the piston and returns the same to theretracted position when the first mentioned means is operated to exhaustthe cylinder followed by exhaust of said built-up pressure through saidlimited leakage guideway.

12. In combination:

a. a single stroke fluid pressure operated motor having a cylinder witha piston operable therein between a retracted position at one end of thecylinder and an actuated position at the other and closed end of thecylinder, and with a driver extended from the piston and through asubstantially close fitting limited leakage guideway at the said otherclosed end of the cylinder;

b. means operable to charge and to exhaust the cylinder at said one endthereof;

c. restraining means normally holding the piston at rest at saidretracted position;

d. a snubber means comprising a body of resilient material surroundingthe driver and with a seat having sealed engagement with the bottom ofthe piston upon arrestment of the piston at said actuated position;

e. a closed fluid reservoir in open and continuous communication withthe cylinder above said snubber seat and below the piston throughout itstravel between said retracted and actuated positions;

f. and air retum means for movement of the piston from said actuatedposition to said retracted position when the first mentioned means isoperated to exhaust the cylinder and comprising, a fluid restrictingcheck valve through and opening above the bottom of the piston andcommunicating with the fluid under pressure advancing the piston andopen into said reservoir when the first mentioned means is operated tocharge the cylinder;

g. whereby there is a build-up of fluid pressure in the reservoir as thepiston reaches the said actuated position, and whereby the built-upfluid pressure is applied to the piston and returns the same to theretracted position when the first mentioned means is operated to exhaustthe cylinder followed by exhaust of said built-up pressure through saidlimited leakage guideway.

13. In combination:

a. a single stroke fluid pressure operated motor having a cylinderchamber with an open ended cylinder seated therein to reciprocablyreceive a piston operable between a retracted position at said open endof the cylinder and an actuated position at the other seated and closedend of the cylinder, and with a driver extended from the piston and outof the seated closed end of the cylinder and through a closed fittinglimited leakage guideway in said cylinder chamber;

b. means operable to charge and to exhaust the cylinder at said open endthereof, from fluid pressure stored in said cylinder chamber;

0. restraining means normally holding the piston at rest at saidretracted position;

d. a closed fluid reservoir surrounding the cylinder and in continuouscommunication with the cylinder through an opening therein below thepiston throughout its travel between said retracted and actuatedpositions;

e. and air return means for movement of the piston from said actuatedposition to said retracted position when the first mentioned means isoperated to exhaust the cylinder and comprising, a fluid restrictingport through the piston and communicating with the fluid under pressureadvancing the piston and open into said reservoir below the piston whenthe first mentioned means is operated to charge the cylinder;

f. whereby there is a build-up of fluid pressure in the reservoir as thepiston reaches the said actuated position, and whereby the built-upfluid pressure is applied to the piston and returns the same to theretracted position when the first mentioned means is operated to exhaustthe cylinder followed by exhaust of said built-up pressure through saidlimited leakage guideway.

14. In combination:

a. a single stroke fluid pressure operated motor having a cylinderchamber with an open ended cylinder seated therein to reciprocablyreceive a piston operable between a retracted position at said open endof the cylinder and an actuated position at the other seated and closedend of the cylinder, and with a driver extended from the piston and outof the seated and closed end of the cylinder and through a close fittinglimited leakage guideway in said cylinder chamber;

b. means operable to charge and to exhaust the cylinder at said open endthereof, from fluid pressure stored in said cylinder chamber;

c. restraining means normally holding the piston at rest at saidretracted position;

d. a closed fluid reservoir surrounding the cylinder and in continuouscommunication with the cylinder through an opening therein below thepiston throughout its travel between said retracted and actuatedpositions;

e. and air return means for movement of the piston from said actuatedposition to said retracted position when the first mentioned means isoperated to exhaust the cylinder and comprising, a fluid restrictingcheck valve means through the piston and communicating with the fluidunder pressure advancing the piston and open into said reservoir belowthe piston when the first mentioned means is operated to charge thecylinder;

. whereby there is a build-up of fluid pressure in the reservoir as thepiston reaches the said actuated position, and whereby the build-upfluid pressure is applied to the piston and returns the same to theretracted position when the first mentioned means is operated to exhaustthe cylinder followed by exhaust of said built-up pressure through saidlimited leakage guideway.

l5. ln combination:

a. a single stroke fluid pressure operated motor having a cylinderchamber with an open ended and externally flanged cylinder seatedtherein to reciprocably receive a piston operable between a retractedposition at said open and flanged end of the cylinder and an actuatedposition at the other seated and closed end of the cylinder, and with adriver extended from the piston and out of the seated end of thecylinder and through a substantially close fitting limited leakageguideway in said cylinder chamber;

b. means operable to charge and to exhaust the cylinder at said open andflanged end thereof, from fluid pressure stored in said cylinderchamber;

c. restraining means normally holding the piston at rest at saidretracted position;

d. a snubber means comprising a body of resilient material surroundingthe driver and with a seat having sealed engagement with the bottom ofthe piston during its arrestment at the actuated position;

. a closed fluid reservoir defined by the seated end and flanged end ofthe cylinder engaging the cylinder chamber and in open and continuouscommunication with the cylinder through an opening therein above saidsnubber seat and below the piston throughout its travel between saidretracted and actuated positions;

f. and air return means for movement of the piston from said actuatedposition to said retracted position when the first mentioned means isoperated to exhaust the cylinder and comprising, a fluid restrictingport through and opening above the bottom of the piston andcommunicating with the fluid under pressure advancing the piston andopen into said reservoir when the first mentioned means is operated tocharge the cylinder;

. whereby there is a build-up of fluid pressure in the reservoir as thepiston reaches the said actuated position, and whereby the built-upfluid pressure is applied to the piston and returns the same to theretracted position when the first mentioned means is operated to exhaustthe cylinder followed by exhaust of said built-up pressure through saidlimited leakage guideway.

1. A pneumatically operated fastener driving tool comprising a housing having a cavity defining a fluid reservoir, a cylinder in said housing, a piston slidably mounted in said cylinder, a cylinder valve means for controlling the admission of fluid and for the exhaustion of fluid from one end of said cylinder, a piston return reservoir in said housing, air passage means connecting said piston return reservoir and said cylinder and including port means opening in sAid cylinder adjacent the other end thereof, said piston including a pair of spaced peripheral grooves in its outer wall, a ring sealing member in the one of said grooves toward said one end of said cylinder effecting a pneumatic seal between said piston and said cylinder, air passage means in said piston extending from the other of said grooves around said one of said grooves and including means defining ports in said other of said grooves, a resilient ring sealing member in said other of said grooves normally seated against said ports and expandable upon a selected pressure differential between said one end of said cylinder and said other end thereof to unseat from said ports to provide for fluid to bypass around the first sealing member from said one end of said cylinder to said other end thereof providing for passage of air into said piston return reservoir.
 2. A fastener driving tool as set forth in claim 1 wherein said last mentioned sealing member is an O-ring.
 3. A fastener driving tool as set forth in claim 2 wherein the inside diameter of said O-ring in its unstressed state is less than the minimum diameter of said other of said grooves, and the diametrical thickness of said O-ring is less than the width of said other of said grooves.
 4. A fastener driving tool as set forth in claim 1 wherein said piston is generally cup-shaped with a central cavity opening toward said one end of said cylinder and said air passage means comprises a plurality of passageways communicating between the inner surface of said other of said grooves and said cavity.
 5. A fastener driving tool as set forth in claim 1 and including a resilient annular bumper adjacent said other end of said cylinder engageable by said piston and defining a pneumatic seal when said piston is at said other end of said cylinder.
 6. A fastener driving tool as set forth in claim 1 wherein said cylinder is provided with an enlarged diameter portion at its upper end defining a shoulder, and wherein said ring sealing member sets above said shoulder when said piston is in its normal position to retain the piston in said normal position.
 7. A pneumatically operated fastener driving tool comprising a housing having a cavity defining a fluid reservoir, a cylinder in said housing having an open upper end and an enlarged diameter portion forming a shoulder with the remainder of said cylinder and extending from said shoulder to the open upper end of the cylinder, a piston slidably mounted in said cylinder and provided with at least one peripheral groove in its outer wall, a ring sealing member in said groove effecting a pneumatic seal between said piston and said cylinder and setting above said shoulder when said piston is in its normal position thereby holding said piston in said normal position, a cylinder valve means for controlling the admission of fluid and the exhaustion of fluid from the open upper end of said cylinder, said cylinder valve means including structure engaging the piston to stop the piston in said normal position, the shoulder in the cylinder being spaced downwardly from the open upper end thereof a distance such that the ring sealing member rests on the shoulder when the piston engages the structure on the cylinder valve means, and means controlling operation of said cylinder valve.
 8. In combination: a. a single stroke fluid pressure operated motor having a cylinder with a piston operable therein between a retracted position at one end of the cylinder and an actuated position at the other and closed end of the cylinder, and with a driver extended from the piston and through a close fitting limited leakage guideway at the said other closed end of the cylinder; b. means operable to charge and to exhaust the cylinder at said one end thereof; c. restraining means normally holding the piston at rest at said retracted position; d. a closed fluid reservoir in open and continuous communication with the cylinder below the piston throughout its travel between said Retracted and actuated positions; e. and air return means for movement of the piston from said actuated position to said retracted position when the first mentioned means is operated to exhaust the cylinder and comprising, a fluid restricting port through the piston and communicating with the fluid under pressure advancing the piston and open into said reservoir below the piston when the first mentioned means is operated to charge the cylinder; f. whereby there is a build-up of fluid pressure in the reservoir as the piston reaches the said actuated position, and whereby the built-up fluid pressure is applied to the piston and returns the same to the retracted position when the first mentioned means is operated to exhaust the cylinder followed by exhaust of said built-up pressure through said limited leakage guideway.
 9. In combination: a. a single stroke fluid pressure operated motor having a cylinder with a piston operable therein between a retracted position at one end of the cylinder and an actuated position at the other and closed end of the cylinder, and with a driver extended from the piston and through a close fitting limited leakage guideway at the said other closed end of the cylinder; b. means operable to charge and to exhaust the cylinder at said one end thereof; c. restraining means normally holding the piston at rest at said retracted position; d. a closed fluid reservoir in open and continuous communication with the cylinder below the piston throughout its travel between said retracted and actuated positions; e. and air return means for movement of the piston from said actuated position to said retracted position when the first mentioned means is operated to exhaust the cylinder and comprising, a fluid restricting check valve means through the piston and communicating with the fluid under pressure advancing the piston and open into said reservoir below the piston when the first mentioned means is operated to charge the cylinder; f. whereby there is a build-up of fluid pressure in the reservoir as the piston reaches the said actuated position, and whereby the built-up fluid pressure is applied to the piston and returns the same to the retracted position when the first mentioned means is operated to exhaust the cylinder followed by exhaust of said built-up pressure through said limited leakage guideway.
 10. In combination: a. a single stroke fluid pressure operated motor having a cylinder with a piston operable therein between a retracted position at one end of the cylinder and an actuated position at the other and closed end of the cylinder, and with a driver extended from the piston and through a close fitting limited leakage guideway at the said other closed end of the cylinder; b. means operable to charge and to exhaust the cylinder at said one end thereof; c. restraining means normally holding the piston at rest at said retracted position; d. a closed fluid reservoir in open and continuous communication with the cylinder below the piston throughout its travel between said retracted and actuated positions; e. and air return means for movement of the piston from said actuated position to said retracted position when the first mentioned means is operated to exhaust the cylinder and comprising, a port through the piston and communicating with the fluid under pressure advancing the piston, a valve seat surrounding the piston and carrying a constricted check valve element to yieldingly open the port into the cylinder below the piston and into said reservoir when the first mentioned means is operated to charge the cylinder; f. whereby there is a build-up of fluid pressure in the reservoir as the piston reaches the said actuated position, and whereby the built-up fluid pressure is applied to the piston and returns the same to the retracted position when the first mentioned means is operated to exhaust the cylinder followed by exhaust of said built-up pressure through said limited leakAge guideway.
 11. In combination: a a single stroke fluid pressure operated motor having a cylinder with a piston operable therein between a retracted position at one end of the cylinder and an actuated position at the other and closed end of the cylinder, and with a driver extended from the piston and through a substantially close fitting limited leakage guideway at the said other closed end of the cylinder; b. means operable to charge and to exhaust the cylinder at said one end thereof; c. restraining means normally holding the piston at rest at said retracted position; d. a snubber means comprising a body of resilient material surrounding the driver and with a seat having sealed engagement with the bottom of the piston upon arrestment of the piston at said actuated position; e. a closed fluid reservoir in open and continuous communication with the cylinder above said snubber seat and below the piston throughout its travel between said retracted and actuated positions; f. and air return means for movement of the piston from said actuated position to said retracted position when the first mentioned means is operated to exhaust the cylinder and comprising, a fluid restricting port through and opening above the bottom of the piston and communicating with the fluid under pressure advancing the piston and open into said reservoir when the first mentioned means is operated to charge the cylinder; g. whereby there is a build-up of fluid pressure in the reservoir as the piston reaches the said actuated position, and whereby the built-up fluid pressure is applied to the piston and returns the same to the retracted position when the first mentioned means is operated to exhaust the cylinder followed by exhaust of said built-up pressure through said limited leakage guideway.
 12. In combination: a. a single stroke fluid pressure operated motor having a cylinder with a piston operable therein between a retracted position at one end of the cylinder and an actuated position at the other and closed end of the cylinder, and with a driver extended from the piston and through a substantially close fitting limited leakage guideway at the said other closed end of the cylinder; b. means operable to charge and to exhaust the cylinder at said one end thereof; c. restraining means normally holding the piston at rest at said retracted position; d. a snubber means comprising a body of resilient material surrounding the driver and with a seat having sealed engagement with the bottom of the piston upon arrestment of the piston at said actuated position; e. a closed fluid reservoir in open and continuous communication with the cylinder above said snubber seat and below the piston throughout its travel between said retracted and actuated positions; f. and air return means for movement of the piston from said actuated position to said retracted position when the first mentioned means is operated to exhaust the cylinder and comprising, a fluid restricting check valve through and opening above the bottom of the piston and communicating with the fluid under pressure advancing the piston and open into said reservoir when the first mentioned means is operated to charge the cylinder; g. whereby there is a build-up of fluid pressure in the reservoir as the piston reaches the said actuated position, and whereby the built-up fluid pressure is applied to the piston and returns the same to the retracted position when the first mentioned means is operated to exhaust the cylinder followed by exhaust of said built-up pressure through said limited leakage guideway.
 13. In combination: a. a single stroke fluid pressure operated motor having a cylinder chamber with an open ended cylinder seated therein to reciprocably receive a piston operable between a retracted position at said open end of the cylinder and an actuated position at the other seated and closed end of the cylinder, and with a driver extended from the piston and out of the seAted closed end of the cylinder and through a closed fitting limited leakage guideway in said cylinder chamber; b. means operable to charge and to exhaust the cylinder at said open end thereof, from fluid pressure stored in said cylinder chamber; c. restraining means normally holding the piston at rest at said retracted position; d. a closed fluid reservoir surrounding the cylinder and in continuous communication with the cylinder through an opening therein below the piston throughout its travel between said retracted and actuated positions; e. and air return means for movement of the piston from said actuated position to said retracted position when the first mentioned means is operated to exhaust the cylinder and comprising, a fluid restricting port through the piston and communicating with the fluid under pressure advancing the piston and open into said reservoir below the piston when the first mentioned means is operated to charge the cylinder; f. whereby there is a build-up of fluid pressure in the reservoir as the piston reaches the said actuated position, and whereby the built-up fluid pressure is applied to the piston and returns the same to the retracted position when the first mentioned means is operated to exhaust the cylinder followed by exhaust of said built-up pressure through said limited leakage guideway.
 14. In combination: a. a single stroke fluid pressure operated motor having a cylinder chamber with an open ended cylinder seated therein to reciprocably receive a piston operable between a retracted position at said open end of the cylinder and an actuated position at the other seated and closed end of the cylinder, and with a driver extended from the piston and out of the seated and closed end of the cylinder and through a close fitting limited leakage guideway in said cylinder chamber; b. means operable to charge and to exhaust the cylinder at said open end thereof, from fluid pressure stored in said cylinder chamber; c. restraining means normally holding the piston at rest at said retracted position; d. a closed fluid reservoir surrounding the cylinder and in continuous communication with the cylinder through an opening therein below the piston throughout its travel between said retracted and actuated positions; e. and air return means for movement of the piston from said actuated position to said retracted position when the first mentioned means is operated to exhaust the cylinder and comprising, a fluid restricting check valve means through the piston and communicating with the fluid under pressure advancing the piston and open into said reservoir below the piston when the first mentioned means is operated to charge the cylinder; f. whereby there is a build-up of fluid pressure in the reservoir as the piston reaches the said actuated position, and whereby the build-up fluid pressure is applied to the piston and returns the same to the retracted position when the first mentioned means is operated to exhaust the cylinder followed by exhaust of said built-up pressure through said limited leakage guideway.
 15. In combination: a. a single stroke fluid pressure operated motor having a cylinder chamber with an open ended and externally flanged cylinder seated therein to reciprocably receive a piston operable between a retracted position at said open and flanged end of the cylinder and an actuated position at the other seated and closed end of the cylinder, and with a driver extended from the piston and out of the seated end of the cylinder and through a substantially close fitting limited leakage guideway in said cylinder chamber; b. means operable to charge and to exhaust the cylinder at said open and flanged end thereof, from fluid pressure stored in said cylinder chamber; c. restraining means normally holding the piston at rest at said retracted position; d. a snubber means comprising a body of resilient material surrounding the driver and with a seat having sealed engagement With the bottom of the piston during its arrestment at the actuated position; e. a closed fluid reservoir defined by the seated end and flanged end of the cylinder engaging the cylinder chamber and in open and continuous communication with the cylinder through an opening therein above said snubber seat and below the piston throughout its travel between said retracted and actuated positions; f. and air return means for movement of the piston from said actuated position to said retracted position when the first mentioned means is operated to exhaust the cylinder and comprising, a fluid restricting port through and opening above the bottom of the piston and communicating with the fluid under pressure advancing the piston and open into said reservoir when the first mentioned means is operated to charge the cylinder; g. whereby there is a build-up of fluid pressure in the reservoir as the piston reaches the said actuated position, and whereby the built-up fluid pressure is applied to the piston and returns the same to the retracted position when the first mentioned means is operated to exhaust the cylinder followed by exhaust of said built-up pressure through said limited leakage guideway. 